Cigarette filters



June 22, 1965 D. T. DUNLAP 3,190,294

CIGARETTE FILTERS Filed Sept. 30, 1958 United States Patent Ofi iceddfifilfid Patented June 22, 1965 3,1ltl,294 (ZEGARETTE FILTERS DonaldT. Dunlap, Charlotte, N.C., assignor to Celanese Corporation of America,New York, N.Y., a corporation of Delaware Filed Slept. 30, N58, Ser. No.764,338 5 (Ilaims. (Cl. 131-293) The present invention relates to anovel, shape-retaining fibrous material and to a process and apparatuswhereby it can be formed. More particularly, it relates to the formationof a shape-retaining structure of thermoplastic filamentary materialsuitable for use as a cigarette filter plug.

Cellulose acetate has gained wide acceptance as a filter for tobaccosmoke, being incorporated as a mouthpiece on cigarettes. In oneprocedure for manufacturing such cigarettes, a tow or bundle of severalthousand continuous cellulose acetate filaments is spread flat, sprayedwith a plasticizer, brought into a predetermined shape by passagethrough a corresponding shaped aperture in a device referred to as acondenser, and fed into a conventional cigarette wrapping machinetogether with cigarette paper. The paper wraps the tow into a continuousrod and is then secured to maintain the shape in the same manner thattobacco is held in paper to form cigarettes. After the paper-wrappedfilter rod is cut into plugs of the desired length, the plugs are curedto effect stiffening of the filter through bonding of the filaments attheir points of contact and the plugs are incorporated into cigarettesin well-known manner by being wrapped in cigarette paper with tobacco.

By proceeding as outlined, time is consumed in the initial wrapping ofthe tow in paper, and, where the paper is secured by glueing, in theapplication of glue to seal the paper and in the drying of the glue. Inaddition, paper and glue are required which, though not contributing tofiltration, add to the cost of the filter.

In another procedure, a bundle of filaments is heated while being passedthrough a stationary shaping member. The heat is applied in such amountthat the surface filaments are fused to form an impervious sheath. Whilethe sheath serves to retain the shape without a paper wrapping, thefilaments employed in forming the sheath lose their filamentarycharacter and will not contribute to filtration of smoke. The resultingoverall filtration efficiency will thus be lower than for paper wrappedfilters wherein all filaments are effective during filtration.

Accordingly, the primary object of the present invention is theprovision of a novel process and apparatus for the rapid production ofpaperless shape-retaining cigarette filter rods and plugs without lossof the filamentary character of the component filaments.

Other and further objects of the invention will be apparent from thedescription which follows.

In accordance with the present invention, a continuous tow of limpthermoplastic filaments is spread flat and sprayer with a plasticizer,i.e. partial solvent or swelling agent which is preferably non-volatileor an active solvent which is preferably volatile. The plasticized towis then passed through heated grooved movable members such as rollers orwheels which condense the tow into a predetermined transverse shape suchas a circle, ellipse, etc., and heat the surface of the towsufi'iciently to cohere the outermost filaments to each other at theirpoints of contact without destroying their filamentary character. Theheat may be supplied by a quartz tubular heating element or byequivalent heating means.

Although there is movement of the heated grooved rollers or wheels, thesurface of the tow is stationary with respect to those portions of theheated surfaces which shape the same and cohere the surface filamentsthereof.

Non-circular clamping members movable with the tow upon clampingengagement therewith, such as links on an endless chain or belt, mayalso be used to serve the same purpose though circular elements arepreferred since these lead to continuity of operation and more rapidproduction rates. As will now be evident, there is no wiping action ofthe shaping member relative to the filaments and filter elements of highoverall filtration efficiency are rapidly and simply obtained.

Upon cooling the cohered filaments cause the structure to retain theshape it had during heating. The filter rod is then cut into plugs forincorporation into cigarettes.

It is essential in accordance with the invention that the filamentarytow be treated with plasticizer to permit bonding of the superificialfilaments initially under such mild conditions that they will not losetheir filamentary character as in formation of a skin. The plasticizeralso permits curing to be effected without heating so intensely asdisadvantageously to alter the physical character of either the inner orouter filaments.

The invention will now be described more fully with reference to theaccompanying drawing wherein:

FIG. 1 is a schematic elevation of an apparatus for making cigaretteplugs and illustrating the procedure of the present invention;

FIG. 2 is a section taken through the forming and heating rolls alongthe line 2-2 in FIG. 1;

FIG. 3 is a perspective view of a plug produced by the apparatus of FIG.1; and

FIG. 4 is a transverse section on a greatly enlarged scale through aportion of the plug shown in FIG. 3.

Referring now more particularly to the drawing, in FIG. 1 there is showna crimped cellulose acetate tow ll) composed, for example, of 9000continuous filaments of 8 denier. The tow 10 is removed from itsshipping container ill and is opened or spread flat by opener 12 ofconventional construction. The tow 10 then passes continu ously throughbox 13 into which plasticizer is sprayed as a mist, the opened towpicking up the plasticizer. The plasticized tow next advances through acircular guide or condenser 14 toward the heated elements 15.

As can be seen the heating elements 15 are constituted, in the preferredform of the invention which is illustrated, by numerous pairs of smallgrooved rollers or wheels 16, the groove being a peripheral groove 17.in the drawing, two pairs of wheels are placed so that their rotationalplanes are offset at an angle, one in horizontal and the other invertical position. As will be evident, these angles may be varied andmore than two pairs of rollers or wheels may be employed for the purposeof ironing out or eliminating any markings or distortions caused by theforming wheels or rolls. The pairs of rollers or wheels 16 arepreferably closely spaced with respect to one another so that the tow isstill warm on reaching the second pair of rollers and so that formationof a coherent mass can be effected rapidly without repeated heatingwhich would form an unduly thick skin on the surface and would unite theinner filaments at so many points as to reduce the surface area forfiltration and as to form a stiff rigid rod. As will be evident, therollers or wheels in each of the pairs 16 are opposed to one another sothat the filamentary tow is shaped therebetween.

The rollers or wheels 16 may be driven at machine speed, eg at a ratesuch that the peripheral velocity of the wheels, particularly at thebottom of the grooves 17 formed therein, coincides with the linearvelocity of the tow. On the other hand, the rollers or wheels 16 may befree rolling in which event the rate of rotation thereof is controlledby the passage of the tow between the pairs of rollers and other means,such as a conventional cigarette making machine, which is normallydirectly in 3 back of the filter forming unit to take the rod and cut itinto plugs in the manner that wrapped tobacco is cut into short lengths,or driven unheated feed rollers may be employed to pull the filamentary.tow through the heated forming rollers. The grooves in the variouspairs of rollers may all be shaped to define a substantially circularopening of somewhat larger diameter with the trailing pairs of rollersbeing grooved to define a substantially circular opening of somewhatsmaller diameter. 1

In theform of .the invention which is illustrated, the forming rollersor wheels 16 include electric heating elements 13 imbedded therein, anelectrical circuit 19 being employed whereby the forming rollers 16 areheated to filament cohering temperature.

Instead of or in addition to electrical heating, the various pairs ofrollers 16 may be confined within an oven, preferably a radiant heated'oven, and the rollers heated by the heat of the oven. If desired,additional pairs of rollers may be employed to facilitate cooling of therod, these additional rollers or wheels having refrigerant passingtherethrough to assist in the cooling operation. However, and as isillustrated in the'drawin g, air cooling of the shape-retaining rod ispermissible.

The surfaces of the grooves on all of the rollers or wheels'aredesirably coated with a release agent, such as a silicone release agentor these surfaces may be plated or sand blasted to reduce thepossibility that the filamentary tow will stick to the rollers orwheels.

The tow is now in the form of a paperless shape-re.

taining cigarette filter rod 20 which passes to the cutter 21 of aconventional cigarette making machine where it such as at 24 and theyare cohered without loss of their filamentary character so that allfilaments contribute to of heating supplied to the tow by any given pairof rollers 16 is only a fraction 'of a second but the tow remains withinthe desired temperature range for the indicatedtime interval because ofthe close positioning of the successive rollers. a

In making a filter for a cigarette" of conventional size, the tow canrange in denier from about 60,000 to 120,000 and the individualfilaments thereof can range from about 3 to 16 denier. vThe tow employedis preferably a crimped tow having from about 6 to 12 crimps per inch oftow, the length being determined by placing a specimen of the tow. undersufficient tension to remove the crimps therefrom. a

-The following example is given by way of illustrating the practice ofthe present invention.

EXAMPLE A tow of 10,000 continuous filaments, 80,000 total denier, ofcellulose acetate of an acetyl value of 54-56%, having 8-10 crimps perinch based on the tensioned length of the tow,is opened and spread outto a width of '12 to 14 inches and glycerol triacetate is appliedthereto by spraying to the extent of 10% by'weight of the tow.

The plasticized, tow is then passed through the heated rollers 15 asshown in FIG. 1. The surface of the heated rollers which contacts the[tow is maintained at a temperature of about 450 F.-by means of atubularquartz infrared lamp and the plasticized tow is advanced at therate of about 1 /2 feet per second through 4 pairs of the filteringaction. As can be seen in FIG. 4, the outer surface portions of theoutermost filaments are seen to be slightly flattened so as to besubstantially coincident with the continuous closed curve defining theperiphery;

of the filter, i.e., curve 25 shown in broken lines and slightly offsetfor ease of illustration.

The tow can. be formed of any thermoplastic filamentary material such asnylon, linear-polyesters such as polyethyleneterephthalate, and thelike, but the preferred materials are cellulose esters of organic acidsand particularly cellulose acetate, the acetyl value of which can rangefrom about 50 to about 62.5% by weight calculated as acetic acid.

The sprayed plasticizer softens the surfaces of the filaments andpermits cohesive joinder of the outermost filaments under thermalconditions which will not destroy the filamentary character of thefilaments. The composition of the plasticizer will depend up thecomposition of the tow. With cellulose acetate the preferredplasticizers include swelling agents such as glycerol triacetate,triethyl citrate, dimethoXy-ethyl phthalate, methyl phthalyl ethylglycolate, and the like, and. active solvents such as acetone, methylenechloride, dioxane, dirnethyl formamide, and the like. an amount rangingfrom about 3st o 30% by weightof the tow. When the plasticizer comprisesa low boiling solvent preferably only moderate temperatures are utilizedto effect bonding, thereby preventing condensation pick-' up due torapid cooling caused by rapid evaporation of solvent at hightemperatures. Where the plasticizer comprises a swelling agent thetemperature of heatingcan range from about 350 to 600 F. and preferably400 to 500 F. and the duration of heating totalsfrom about one to aboutten seconds. As will be evident, the duration The plasticizer can beapplied in.

freely rotatable rollers successively offset at 90 angles. Each'rolleris 2% inches in diameter. After leaving the last pair of rollers, thetow, which is now a shape-retaining rod about 25 mm. in circumference iscut into'plugs 90 mm. long which plugs are cured at room temperature in2 hours.

Using another swelling agent such as the citrate, phthalate or glycolatenamed hereinabove gives substantially the same results after curing for1 hour at 175 F.

The product is characterized by a smooth surface free of belt imprint.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit of my invention.

Having described my invention what I desire to secure by Letters Patentis:

- onto said opened tow, conveying said plasticized tow- 1. Ashape-retaining cigarette filter plug comprising a plurality of crimpedthermoplastic filaments of total denier ranging from about 60,000 to120,000 and of individual denier ranging from about 3 to 16, all of saidfilaments because of their crimp contacting other fila- ,ments at aplurality ofspaced locations, the outermost between a plurality of pairsof rotatable, heated opposed peripherally grooved rollerswhich cooperateto shape said tow into predeterminedconfiguration and to cohere theoutermost filaments of saidtow to each other atftheir points of contactwithout destroying their filamentary character, said rollers beingrotated at a peripheral speed equal tolthe linear speed of said tow inpassing therebetween, the plane in whicheach pair of rollers rotatesbeing offset'relative to the rotationalplanes of adjacent pairs ofrollers, and cooling, and severing said cooled tow into plugs ofpredetermined length to produce a cigarette filter plug of high overalfiltration efficiency. 4. The process recited in claim 3 in which about3 to 30% by weight of said plasticizer is applied to said tow.

5. Apparatus for forming shape-retaining paperless cigarette filterplugs from a continuous tow of limp thermoplastic filaments, comprisingmeans for opening said tow, means for applying plasticizer to saidopened tow, a plurality of pairs of heated opposed peripherally groovedrollers for shaping said tow into predetermined configuration wherebythe outermost filaments of said tow are caused to cohere to each otherat their points of contact without destroying their filamentarycharacter, the plane in which each pair of rollers rotates being olfsetrelative to the rotational plane of adjacent pairs of rollers, means foradvancing said tow between said pairs of rollers at a linear speed equalto the peripheral speed of said rollers, and means for severing said towinto plugs of predetermined length to produce a cigarette filter plug ofhigh overall filtration efliciency.

References Cited by the Examiner UNITED STATES PATENTS 163,893 7/55Australia.

1 EARL M. BERGERT, Primary Examiner.

0 C, F. KRAFFT, R. LEIBOWITZ, Examiners.

1. A SHAPE-RETAINING CIGARETTE FILTER PLUG COMPRISING A PLURALITY OFCRIMPED THERMOPLASTIC FILAMENTS OF TOTAL DENIER RANGING FROM ABOUT60,000 TO 120,000 AND OF INDIVIDUAL DENIER RANGING FROM ABOUT 3 TO 16,ALL OF SAID FILAMENTS BECAUSE OF THEIR CRIMP CONTACTING OTHER FILAMENTSAT A PLURALITY OF SPACED LOCATIONS, THE OUTERMOST FILAMENTS BEINGPLASTICIZED AND COHERED INTO A SHAPERETAINING SURFACE WITHOUT LOSS OFTHEIR FILAMENTARY CHARACTER, SAID PLUG HAVING A SMOOTH SURFACE.